A solenoid typically comprises a body comprised of steel which has wire wrapped around the body in a coiled fashion. The body has an aperture with a plunger located in a slidable fashion in the aperture. An electric current is applied to the coil which creates a magnetic field. As the current is applied, the plunger is caused to slide in the aperture due to the magnetic field created by the coil. As the plunger moves into the body, an air gap in the aperture is filled. As the air gap is filled, the spacial gap between the lines of the magnetic field diminishes which in turn increases the strength of the field. Therefore, as the plunger moves into the body, its velocity tends to increase due to an enhanced magnetic field. Because of the high velocity of the plunger, a solenoid system may be damaged by the repeated impact of the high speed plunger. Moreover, the impact of the plunger against the body of the solenoid creates a rather loud noise.
Compressible pads or springs have been used in an attempt to absorb some of the energy of the plunger. As the plunger moves inwardly toward the solenoid body, abutments extending from the plunger or body impact the pads or springs. The impact causes the pads or springs to compress and eventually stop the plunger. U.S. Pat. No. 2,311,890 is representative of this system. However, a problem encountered with the pad or spring systems is a lack of precision in the travel distance of the plunger. This is particularly true of solenoids used in embossing. As the plunger impacts the pad or spring, its precise point of stopping will vary according to the force applied by the plunger during the embossing process since different characters require different embossing forces. Also, the age of the spring or pad or climatic conditions affect the elastic properties of the pad. Moreover, as the springs or pads deteriorate, the resistive force afforded by the springs or pads tends to lessen and thus allows the plunger to travel further into the core.
Another problem encountered with the use of pads or springs is that their placement in the magnetic gap may require increasing the magnetic gap thereby decreasing the force of the solenoid. In addition, the additional iron or metal of the abutments or springs may create interference in the magnetic field. This interference in the magnetic field results in a lack of precision in the travel distance of the plunger. The present invention solves these and other problems associated with the prior art.